Melamine and melamine cyanurate are well-known flame retardant compounds conventionally used as an additive to polymers and polymeric blends.
However, melamine and melamine cyanurate are solid and therefore not easy to use. If melamine is used as an additive in polymeric blends, melamine will settle out of the system due to its solid particles. In spray-rigid foam systems, for instance, the melamine solid particles will clog the spray gun nozzle.
Some liquid flame retardants, such as halogen-containing or phosphorous-containing chemicals, can be used as additives; however, halogen- or phosphorous-containing chemicals are toxic, corrosive and generally more expensive than melamine and melamine cyanurate, whereas melamine is a non-halogen, non-phosphorous, non-toxic, non-corrosive and generally less expensive chemical.
JP 1495362 describes a fire-retardant polyester obtained by thermally polymerizing thermoplastic polyester forming monomers with added melamine and cyanuric acid; the process makes use of an equi-molar amount of cyanuric acid and melamine, thereby forming a complex compound which is melamine cyanurate complex; the resulting mixture is polymerized in the presence water at 200-300° C. to provide a polyester containing melamine cyanurate uniformly and finely dispersed in the polyester. Since melamine is totally neutralized by cyanuric acid, therefore, there is no —NH2 group to react onto the polymer backbone, whereby solid melamine cyanurate acts as an additive in the polyester.
EP 376 380 relates to an aromatic polymer with a liquid-crystalline behavior including one or more tri-functional triazine units. The described process contemplates reacting aromatic polyester forming monomers and adding a triazine when the polymer reaches the desired degree of polymerization. It is disclosed that the addition of a small amount of triazine (melamine) can improve the mechanical properties and thermal shock resistance of the obtained liquid-crystal high molecular weight polymer.
WO 2014/135712 describes a process for preparing a high molecular weight polyester which comprises reacting a dicarboxylic acid and a diol in the presence of a triazine derivative. The concentration of triazine derivative, which is determined by the concentration of nitrogen atoms, is generally from 1,000 ppm to 10,000 ppm with a preferred concentration of from 1,000 ppm to 2,500 ppm. The addition of a small amount of melamine derivatives is described as suitable to improve high molecular weight polymer crystallization rate.
An object of the present invention is to provide a polyester (polyol) having flame-retardant properties, wherein melamine is synthetized onto the polyester backbone.
Another object of the invention is to provide a novel polyester which is suitable to react with isocyanate to form polyurethane or polyisucyanurate that can be used, among the others, for rigid foam, spray foam, flexible foam, cast elastomers, TPU (thermoplastic polyurethane), adhesives, coatings, sealants, fiber applications, in order to obtain flame retardancy.